Safety down limit switch for cable hoists



Dec. 1, 1953 J. A. WESTERN SAFETY DOWN LIMIT SWITCH FOR CABLE HOISTS Filed July 15, 1950 2 Sheets-Sheet l INVENTOR v/fiMfS 4. wes'rERN. BY

W L/A AM ATTQRNEYS Dec. 1, 1953 J. A. WESTERN 2,661,405 SAFETY DOWN LIMIT SWITCH FOR CABLE HOISTS Filed July 15, 1950 2 Sheets-Sheet 2 L I. L 5

. INVENTOR. James 19. wzsrsed WM m 4 'r-r eueys.

Patented Dec. 1, 1953 SAFETY DOWN LIMIT SWITCH FOR.

CABLE HOISTS James A. Western, Detroit, Mich., assignor to Detroit Hoist and Machine Company, Detroit, Mich., a corporation of Michigan Application July 13, 1950, Serial No. 173,621

1 Claim. 1

This invention relates to cable hoists, and more particularly to a safety down limit switch for a cable hoist.

Normally cable hoists of this type are provided with an uplimit safety switch to stop the hoist motor automatically when the hoisting block reaches its uppermost position. When the hoist was operated by a manual switch to control unwinding of the cable, in the event that the operator did not stop the downward movement of the hoisting block it would automatically begin to rewind after the drum had completely unwound the cable thereon. By inadvertent or careless failure to deenergize the electric motor controlling the downward movement of the hoist block, the cable would automatically rewind again raising the block to its uppermost position. The conventional operation of the up limit switch by the block when it reached its uppermost position would be ineffective to deenergize the hoist motor as long as the remote control manual down switch was active. This would result in continued upward movement of the block causing the cable to break with consequent damage to property and endangering of the lives of others.

It is the principal object of the present invention to provide a safety down limit switch which would cause automatic deenergization of the hoist motor at the completion of the unwinding of the cable from the drum.

It is the further object of the present invention to provide a safety limit switch which is normally connected in the electrical circuit to the hoist operating motor and which is adapted for operative engagement with the cable as it starts to rewind for automatically breaking said electrical circuit and stopping the motor.

These and other objects will be seen from the following specification and claim in conjunction with the appended drawings in which:

Fig. 1 is a side elevational view of a portion of the cable hoist shown in Fig. 4 with the rotatable drum thereof sectioned for illustration.

Fig. 2 is a bottom plan view of the down safety limit switch and its mounting and actuating mechanism, shown on an enlarged scale.

Fig. 3 is an elevational view thereof viewed from the upper end of Fig. 2.

Fig. 4 is an elevational view of the hoist with the safety down limit switch mounted thereunder; and

Fig. 5 is a wiring diagram showing the hoist motor, the load lines adapted for connection thereto, the manual control switches for operating additional switch mechanism for regulating the connections of the load lines with the hoist controlling motor for energizing the same and determining its direction of rotation.

It will be understood that the above drawings illustrate merely a preferred embodiment of the invention, and that other embodiments are contemplated within the scope of the claims hereafter set out.

The hoist mechanism shown in Figs. 1 and 4 includes the hoist housing It! which includes the electric reversible motor 21 and the rotary cable winding drum M which is connected to the shaft 21' of said motor in any conventional fashion such as by suitable pulleys and a connecting belt or by sprockets upon the respective shafts of the motor and drum with a chain interconnecting the same.

The driving connection between motor 21 and the rotatable drum [4' is conventional, and for this reason further illustration of this drive is believed unnecessary. A suitable inverted hook 29 projects from the upper portion of the hoist housing providing a means for supporting the same.

The flexible cable I2 is anchored at one end at l3 within the housing In and is looped downwardly with its lowermost portion supporting the load block 25 with depending hook 26, and with the other end of the cable l2 joined to the rotatable drum M at I 5 as shown in Fig. 1.

It will be noted that in Fig. 4 the cable I2 is shown fully wound upon the drum I4, whereas in Fig. l the cable has been fully unwound and has begun to be rewound upon the drum 14.

A down safety limit switch construction is provided secured to the under side of the hoist It with the movable portion thereof in spaced relation to the cable l2 while it is wound upon the drum l4 but which is engageable with the cable as shown in Fig. 1 after the same-has been fully unwound and has just begun to rewind upon said drum.

The down safety limit switch construction includes the rectangular mounting plate I which is shown in enlarged scale in Fig. 2 and which is provided with transverse openings 33 by which the said plate is secured to the under side of the hoist as by the bolts 34 shown in Fig. l.

A pair of spaced downwardly depending flanges 2 and 3 extend from the forward portion of plate I, which flanges are provided with openings to receive the spaced horizontally extending bolts l and 5 which are secured thereto by the lock nuts 6 and i in the manner illustrated in Fig. 2.

Limit switch actuating bar I0 is apertured at its opposite ends for mounting slidably upon the two bolts 4 and 5 with the outward positioning 'of said plate limited by the heads H upon said bolts. Coiled springs 8 and 9 are mounted around the bolts 4 and 5 and are interposed between lock nuts I and the inner surface of the plate 10 for 1 4 f The down limit S i e normally cisd ]out gincludes. thefrecip'rocalplunger-ff!"l which is :adapted to open said li mit' switch, the outer end normally maintaining said plate in its outward position as shown in Fig. 2.

It will be noted thatthe plate is arranged normally, .qi thejcable l2 andin spaced relation thereto when the cable is wound upon the drum I4 as shown in Fig. 4; however the plate will a he manner 'illusfiratd r'ig. 5 the down 'f'sare limit switch eis connectedin the t circu'i't which controls rotation of the motor 2! to cause unwinding bf thjecable er said piuhgetet in engagement with the movable control plate 1 ii.

. j showh fdottec h e mirigg i thereji s provided a conventlonal up safety limit switch 18 wh ch re os io ed .with nf eho t h i and which is engageable'by the bl its uppermost position for auto matically deenergiZ- ing the electric motor-'2'! in its driving jo'f the upward windingmovement ofthe cable drum l4. v This up safety'limit'sw'itch is conventional and is interposed in the electrical circuit as shown'in Fig. 5 f or automatically deenergizing the electric motor Elwhen the hoist'block'25 has reached a predetermined uppermost position.

It is apparent that'in tlie'absenc'e of thepresem down safety limit switch, if the meter was fhot manually 'deenergized'when thec able was completely unwound from the drum, said cable would b'e'gin'to rewind causing elevation'of'the block 25 untilthej cable broke because actuation of this tip safety liinit switch would-not inthis "case denergi'ze' said motor.

As'illustrate'din 'igs. 4 and 5 "there is'iprovided a remote 'c'dh'tiol" station 'or housing "'30 'wl'iich includes a'pair of push-buttons or-s witch controls 3| and 32. Bilttfiniilb'eing adapted to' bntiol br energize the motor '21 for caus'ingiipwa'rd movement or the 1310 1525 whereas button 32 is'ad'a'pt'ed to reverse the operation of the'm'otor zrto'cause downward rhcvehh'entbr the block 25.

.As shown in Fig. 5' button 3! is'joindto coht oi plate 25 for closing the circuit between contact points .2! 'and22 Whereas the control plate 19 is connected to thepush button 32 for closing -'the circuit between contact points 23 and'2'4 .Generallythe push buttons 3|"and 32""are adapted for effecting energization' of the electric motor 2'? for rotating the same in one direction or another. It is seen that safety limit switch "l8is arranged in the electrical circuit, associated'with push button 3! for controlling upward movement of the block 25. and: will be automatically opened opening said circuit. if and when the block 25rises above a predetermined position to engage said up limit switch designated in Fig. 4.

Upon the other. hand the down safety? limit I switch 16 is arranged in the 'electrical'cir'cuit to p the motor 21 which is associated with the down push button 32 in Fig. 5. Y For the purpose of the present'applicati'on' the down safety limit switch construction is actuated by engagement of the cable I2 with the control plate which in turndepresses the limit switch plunger n, in fiect opening the limit switch H5 or the circuit in which 'it is connected 'for deenergizing the motor when it is being operated for lowering the cable block 25.

"As the motori'l is reversible it is necessary that airel'ay switch mechanism be employed which is adapted to change and reverse the electrical conjnections between the power lines Ll, L2 and L3 'ahdfthetermiha sbr motor 21.

While the particular mechanism for the relay terms no par't'er the present invention the electrical connections therefor are diagrammatically indicated in Fig. 5, with the relay switch housing being generally indicated by the numeral 28. Naturally various types of electrical connections could be employ'd responsive 'tothe push buttons 3| and 32 for efiecting reversals in the direction of'ro tation of themotor '2"|,-'and it'is understood 'that the illustration of connections within "the housing '28 of EigJEa shows one Way ofa'ccomplis'hin this reversal. *Push button 3| through plate *26 and cont'acts 2 I and-'22 and the connected'l'e'ad wires are 'ad'aptedtoenergize the magnetic control 35 for the relay switch'35' to cause rotation of motor 'Zlin'su'ch "direction as to cause winding "of the'cable' l 2' o'n-the'drui'n l4.

O'n'the 'oth'er'liand push butt0n'32; plate I 9' and contacts'23"and24 are adapted't'o energize'the 'magnetic control 35 which regulates the relay switch 36"to establish a reversed electrical conn'ection'to motor El'to'rever'se its direction of rotation.

Having described my "invention reference should now be hadto' the'claim'which' followsfor "determining the'sc'ope thereof.

*1 claim: 'In' a safety devicefor a cable hoist,'a-mounting plate adapted 'to'be secured upon the'underside-of said hoist adjacent itscable, a' normally closed limit switch mount'ed 'upon said 'plate; a movable limit switch actuating f plunger pin projecting therefrom, a" pair or spaced stationary supports projecting from saidmounting plate; a-fiat pla te of rectangular cross-section transversely apertured' to 'slidably receive said supports and movably-mounted thereon'adjacent said switch and normally "engaging said plunger pin, arranged transversely 'of' and in "spaced relation to said cable upon unwinding thereof and engageable by said cable as it 'rewinds for opening said limit switch, means on said stationary supports I limiting the outward positioning'of said plungerengaging plate; and coiled springs on said'supborts interposed between saidmounting plate and "said plunger engaging platenormally urging said {plunger-engaging plate into its outwardnonactuating eposition.

JAMES A. 'WESTERN.

Iiferehces cited in the file-of' this patent "UNITED STATES PATENTS Number I Name Date 7 7592 01 lStratton l vlay' 3,1904 1,975,094 Fitch Oct. 2,1934 2 ,982,339 Ehrenfeld Nov. 2711934 "Q12, 2 48;Q10 jN elles 'July 1,1941 gg segz-qs Height septa, '19'41 ij 2 266, 6 Sloan Dec/16,1941 2,365,141 Sully 'Dec. 12, 1944 2,528,581 'Craton "Nov. 7;19'50 

